This work is a study on phonon modes of polycrystalline La1−xCaxMn1−yLiyO3(x = 0.1 − 0.5) by far infrared (FIR) spectroscopy. Samples were prepared by a conventional solid state reaction method. Lithium is a volatile element which can cause changes in the FIR spectra of compared to the spectra of La1−xCaxMn0.9Li0.1O3. The far infrared spectra show that the external mode [La(Ca)] - [Mn(Li)O3], the O - Mn(Li) - O bending mode and Mn(Li) - O stretching mode behave similarly and increase in energy as the Ca concentration increases. The Li+ ion is lighter than the Mn3+ ion and its ionic radius is slightly larger than that of the Mn3+ ion. Thus Li doping introduces unit cells that are even smaller due the Mn4+ ions radius being smaller than Mn3+. This will lead to new lattice modes. Also the high ionicity of Mn4+ leads to a stronger inter-ion electrostatic interaction. As a result the frequencies of lattice vibrations increase. Some evidence of Li incorporation in the crystal lattice is useful, and Li ion doping has now been detected by our FIR spectroscopic technique. These phenomena are all observed in FIR transmission measurements.
Gao, F., Lewis, R. A., Wang, X. Dou, S. X. (2006). Far infrared Spectra of La1-xCaxMn0.9Li0.1O3. Journal of Physics, 28 143-146.